Frequency response compensating means



NOV. 19, 1946. BROWN 2,411,190

FREQUENCY RESPONSE COMPENSATING MEANS Filed Sept. 14, 1944 INVENTOR. E MRS/Mu B/eanw BY 221 a Patented Nov. 19, 1946 UNITED STATES. PATENTQ- OFFICE FREQUENCY RESPONSE COMPENSATING MEANS Marshall Brown, Chicago, 111. Application September 14, 1944, Serial No. 554,103

14 Claims. (Cl. 179-1) The present invention relates to means for adj ustably controlling or varying the frequency response of any audio amplifier and more particularly one using a piezoelectric unit such as a piezoelectric or crystal microphone in a hearing aid. or a piezoelectric or crystal phonograph pickup.

' People who are hard of hearing have diiferent types of hearing loss and this loss as shown by the audiogram or chart of their threshold of hearing may indicate, in one person, a loss of the high notes of the audio frequency range; in another person, a loss of the low notes thereof; in still another person, a loss in the middle or intermediate frequency; and in still a further person, a straight line loss of all the notes for the extent of th audible range.

Among the objects of the invention is to provide a novel device for adjusting the frequency response so as to give a correction for the particular type of loss desired to be'corrected or compensated for' and particularly to make avery gradual or 'very closely controlled adjustment by' fine gradations'or incremental changes which will be substantially smooth as distinguished from a jump or step adjustment or change;

Other objects, advantages, capabilities, features, or the like are comprehendedby the invention as will later appear, or as are inherently possessed by the invention.

Referring briefly to the drawing:

' Fig. 1 is a diagrammatic view of my invention shown in connection with a crystal unit. and with the compensating means connected to the grid of the input tube and'the grid of another audio tube; L

Fig. 2 is a similar view with the invention similarly connected as in Fig. 1, except with the compensating means connect die the plate of an-. other audio tube;

Fig. 3 is a partial similar view withthe compensating means connected to the screen-grid of any audio tube in the circuit; H

Fig. 4 is a similar view with the invention used with a piezoelectric or crystal phonograph pickup and has the compensating means connected en tirely to the grid of the input tube. l f

Referring more particularly to the drawing,

the embodiments chosen to illustrate the ilIVeIlF tion are shown in connection with a tube I (Fig. 1), or a tube 2 (Fig. 2), or atube 3 (Fig.3), and with a crystal microphone 4, the latter being also connected, on the grid side thereof, to the grid 5 of the tube 6. It is to be understood; even though not shown in Fig; 3, that the microphone 2 A is similarly connected to a tube 6 in the partial diagrammatic showing of Fig. 3. 1

My invention comprises the use of a poten tiometer 7 having an adjustable or sliding contact 8, with the potentiometer connected at an end thereof via conductor 9 to a limiting resistor ill which, in turn, is connected via conductor H to the grid circuit part [2 of the grid 5 and microphone :3, and with the potentiometer connected at the other end thereof via conductor 13 to a condenser l4 and thence via conductor I5 to the grid circuit part [6 of the grid I! of tube I (Fig. 1), or to the plate circuit part I 8 of the platel9. of the tube 2 (Fig. 2), or to the screen grid 26 (Fig. 3). Suitable grounds 2! and 22 are connected to the microphone 4 and the sliding contact 8 for completing the. circuit.

Referring more particularly to Fig. 4 the invention is shown inconnection with a piezoelectric or crystal phonograph pickup 23 which is con nected to ground on one side and via aconductor I2-24l 6 to the grid ll of the tube"! on the other side. With this conductor is shunted a potentiometer which is connected at an end thereof via conductor 9, a limiting resistor It, and conductor II to the conductor part I'L -24; and atthe other end thereof via conductor l3, condenser l4, and conductor [5 to theconductor part 24l6. The potentiometer 7 has an adjustable contact. or slider? connected to ground 22. The pickup 23 may have ,a stylusfor the like 25.

The value of the limiting, resistor It! may be selected to limit the maximum amount of low frequency response cut-off of the microphone 4, or the pickup 2'3. Adjusting the sliding contact 8 along the potentiometer 1. toward the end thereof connected to the limiting resistor I0 effects a smooth graduated control of reducing or cutting down the low frequency response whereby there is a'higher pitch or frequency response at the microphone or pickup, and adjusting theslider 8 along the potentiometer. l.toward the end thereof connected to the condenser. effects a smooth graduated controlfor'reducing or cutting? down the high frequency response whereby there is .a lowerpitch or frequency. response.

' .A piezoelectric crystal is a mechanical vibrator electrically equivalent to a series-resonant circuit, and by varying the value of a resistor, or of a condenser,.or both, shunted across it, its frequency.

response. is accordingly changed.

While I havehereindescribed and upon. the

drawing shown a'few illustrative embodiments of my inventionit is. to be understoodthat the 1. In a device of the character disclosedand.

which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combina- .tion therewith of a circuit including a variable resistor only connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground. A l I 2. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor only connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground, said circuit also including a limiting resistor to limit the maximum value of lowfrequency response cut-off of the unit.

3. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor only connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground, a portion of said resistor being connected in shunt with said unit and the other portion thereof connected with a condenser which is connected to said tube.

4. In a device of the character disclosed and which'has a piezoelectric crystal unit connected to ground and to an amplifying tube, the combination therewith of a circuitincluding a variable resistor only connected'in shunt with said unit to control the frequency response of said microphone, and including an adjustable contact connected to said resistor and to ground, a portion of said resistor being connected in shunt with said unit and the. other portion thereof connected with a condenser-which is connected to said tube, said tube havinga grid and said condenser being connected to said grid.

5. In a device of the character disclosed and i which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor only connected in shunt with, said unit the frequency response of said unit, and including an adjustable contact connected to said resistor, and to ground, a portion of said resistor being connected in shunt with said unit and the other portion thereof connected with a condenser which is connected to said tube, said tubehaving a plate and said condenser beingconnected to saidplate. v 1 6. In a device of the character disclosed and which has a piezoelectric 1 crystal unit connected to ground and an amplifying tube, the'combination therewith of a circuit including, a variable resistor only connected inshunt with saidun'it to control thefre'quency response ;of saidunit, and including an. adjustable contact connected to said resistor and to ground, a portion of. said resistor being connected in shunt with said unit and the other portion thereof 7 connected with a condenser which is connected to said tubefsaid tube having a screen grid and said condenser being connected to said screen grid.

7. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor only connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground, a portion of said resistor being connected in shunt with said unit and the other, portion thereof connected with a condenser which is connected to said tube, said circuit also including a limiting resistor to limit the maximum value of low frequency response cut-off of the unit.

8. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground, a portion of said resistor being connected'in shunt with said unit and the other portion thereof connected with a condenser which is connected to said tube, said tubehavin a grid and said condenser being connected to said grid, said circuit also including a limiting resistor to limit the maximum value of low frequency response cut-off of the unit.

9. In a device of the character disclosed, and which has a piezoelectric unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor. connected in shunt with said unit to control the frequency response of said unit, and including an adjustable contact connected to said resistor and to ground, a portion of said resistor being connected in shunt with said unit and the other portion thereof connected with a condenser which is connected to said tube, said tube having a plate and said condenser being connected to said plate, said circuit'also including a limiting resistor to limit the maximum value of low frequency response cut-off of the unit.

10. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and an amplifying tube, the combination therewith of a circuit including a variable resistor connected in shunt with said unit to control the frequency response of said'unit, and including an adjustable contact connectedto said resistor and to ground, aportion of said resistor being connected'in shunt with said unit and the other portion thereof connected with a condenser which is connected to said tube, said tube having a screen grid and said condenser being connected to said screen grid, said circuit alsoincluding a limiting resistor to limit the maximum value of low frequency response cut-ofi'of the unit; c a 11. Ina device of the character disclosed and which has a piezoelectric crystal unit connected to ground and to an amplifying tube, the combination therewith of i aconnection from said unit to said tube, a circuit including a variable resistor only for shunting said unit to control the frequency response of said unit, and'including' an to ground and to an amplifying tube, the combina tion therewith of a connection from said unit to said tube, a circuit including'a variableresistor shunting said unit to control the frequency response of said unit, and including an adjustable contact which is connected to said resistor and to ground, another portion of said variable resistor being connected to a condenser which is connected to said tube, said tube having a grid and said connection being connected to said grid.

13. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and to an amplifying tube, the combination therewith of a connection from said unit to said tube, a circuit including a variable resistor shunting said unit to control the frequency response of said unit, and including an adjustable contact which is connected to said resistor and to ground, another portion of said variable resistor being connected to a condenser which is connected to said tube, said first mentioned portion of said resistor including a, limiting resistor to limit the maximum value of low frequency response cutoif of said unit.

-14. In a device of the character disclosed and which has a piezoelectric crystal unit connected to ground and to an amplifying tube, the combination therewith of a connection from said unit to said tube, a circuit including a variable resistor only for shunting said unit to control the frequency response of said unit, and including an adjustable contact which is connected to said resistor and to ground, another portion of said variable resistor being connected to a condenser which is connected to said tube, said first mentioned portion of said condenser including a limiting condenser to limit the maximum value of high frequency response cut-off of said unit.

MARSHALL BROWN. 

